1. Field of the Invention
The present invention relates generally to an image processing method, an image processing apparatus, and a computer program product.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile, a copier, a plotter, or a multifunction peripheral having functions of two or more of these apparatuses, an inkjet recording apparatus that is one type of liquid-ejection-recording-type image forming apparatus including, as a recording head, a liquid ejection head which ejects liquid droplets are known, for example.
In a low-resolution image printed by such an inkjet recording apparatus, what is generally referred to as jaggy in which a contour portion has a jagged shape, can appear at a contour portion of a character or a line containing an oblique line. The jaggy is caused by dots arranged in a step-like pattern at the contour portion.
It has been conventionally known that a step-like portion of a contour portion is detected, and addition of or replacement with a small dot is performed when printing an image in which the value of resolution in the main-scanning direction differs from that in the sub-scanning direction (Japanese Laid-open Patent Application No. 2006-326913).
However, the image portion to which a small dot is added is fattened. As a result, thickness of a character or a line to which the image portion belongs changes, which may result in a bump-like lump. When printing an image in which resolution in the main-scanning direction and that in the sub-scanning direction differ from each other, dot size is set based on the direction of lower resolution to prevent production of an anomalous image having a white spot at a solid portion or the like. However, this dot size is too large in the direction of higher resolution.
As a result, a problem arises that a jaggy correction (contour portion correction) of when printing an image with resolution in the main-scanning direction different from that in the sub-scanning direction deteriorates image quality of an oblique line extending in a direction close to the direction of higher resolution.
In view of the above circumstance, there is a need to enhance image quality of an image in which resolution in the main-scanning direction differs from that in the sub-scanning direction.